Field of the Invention
Embodiments of the invention generally relate to methods and compositions for removing a completion fluid filter cake in a wellbore, and more particularly, to methods and compositions for dissolving or removing filter cake material generated by a manganese-tetraoxide-based drilling fluid in a wellbore for optimizing production from a surrounding hydrocarbon bearing formation.
Description of the Related Art
Horizontally/multilaterally-drilled wells have been used to enhance both hydrocarbon recovery and total well productivity from many types of reservoirs. Drilling, workover, and production operations may result in near-wellbore formation damage that in most cases cannot be prevented (e.g., pore plugging by calcium carbonate particles from drilling fluid, drilled solid particles, or particles from the formation).
During well operations, drilling fluids can be lost into the surrounding formation. To prevent this, the drilling fluid is frequently modified such that a small amount of the fluid and solids contained therein form a coating on a wellbore surface (i.e., the formation of a “filter cake”). After the completion of drilling operations, the coating or filter cake is typically removed, and production from the formation can proceed. The process used to remove the filter cake can also be used to remove other types of damage or debris from the wellbore prior to beginning hydrocarbon production.
To facilitate the drilling of horizontal/multilateral wells, weighting materials have been introduced into the drilling fluid to increase the density of the drilling fluid for balancing the hydrostatic pressure and for maintaining stability within the wellbore to minimize formation damage and corrosion in the wellbore. Several weighting materials (e.g., bentonite, barite, calcium carbonate (CaCO3) ilmenite, and hematite) have been used in drilling fluids, each of which has several associated limitations. For example, bentonite and barite are not soluble in hydrochloric acid (HCl), and therefore they may cause formation damage in the wellbore. The specific gravity of CaCO3 (e.g., 2.71) limits its application when a high density drilling fluid is needed to drill deep wells. Due to the partial solubility of barite in concentrated formate brines and the conventional practice not to acidize the wellbore prior to completion of the well, CaCO3 and barite have been excluded as options to increase density of the drilling fluid in many applications.
Manganese tetraoxide (Mn3O4) is a high density, acid-soluble weighting material useful in drilling fluids for drilling high temperature/high pressure (HT/HP) wells. Mn3O4 is spherical in shape and has an average partial size of 1-5 microns and a specific gravity of 4.8, which make it appropriate for drilling deep wells. For example, Mn3O4 has been introduced into potassium formate drilling fluids to overcome the main drawback of potassium formate, which is the production of a brine of density 1.7 g/cm3 (106 lb/ft3). Mn3O4 has also been introduced as a weighting material into oil-based drilling fluids due to its ability to lower the plastic viscosity of the oil-based drilling fluid. A water-based drilling fluid weighted with Mn3O4 and a small amount of CaCO3 has also been formulated for use in a wellbore. CaCO3 has been added to the water-based drilling fluid to control filtration properties of the drilling fluid. The need in the industry for a drilling fluid with high rheological properties has been achieved using Mn3O4 particles.
Mn3O4 particles, however, also present many disadvantages as a weighting material in oil-based or water-based drilling fluids. For example, Mn3O4 particles aggregate up to 20 microns in aqueous and oil-based fluids. Accumulation of these aggregates in the critical near wellbore area can result in stuck pipe and mud cake problems during drilling operations. Dust problems associated with the accumulation of these aggregates have also caused formation damage in the wellbore. Additionally, starch may be present in the filter cake covered Mn3O4 particles, which can contribute to additional particle agglomeration. Thus, addressing the removal of a filter cake formed by a drilling fluid weighted with Mn3O4 particles is essential to ensure the effectiveness of drilling and cleaning operations in the wellbore.
Several cleaning compositions have been developed to remove the filter cake generated by a manganese-tetraoxide-based drilling fluid from the wellbore and to minimize formation damage in the wellbore using live acids, gelled acids, strongly buffered organic acids, chelating agents, oxidizing agents, enzymes, in-situ generated organic acids, microemulsions, or combinations of these chemicals. Because Mn3O4 is a strong oxidizing agent having an active phase (i.e., a tetragonal symmetry, non-stoichiometry behavior) locally composed of an octahedral Mn2O3 phase and a tetrahedral MnO phase, it experiences complex interactions with most cleaning fluids, including the aforementioned chemicals. For example, organic acids and chelating agents will not independently dissolve Mn3O4-based filter cakes. Ethylene diamine tetracetic acid (EDTA) at high pH (e.g., a pH of 12) and acetic, propionic, butyric, and gluconic acids at low pH (e.g., a pH of 3-5) exhibit very low solubility. Glutamic, citric, oxalic, and tartaric acids produce white precipitation when reacted with Mn3O4 particles. Similarly, diethylene triaminen pentaacetic acid (DTPA) precipitates manganese silicate if used to dissolve Mn3O4-based filter cake in a sandstone formation.
Citric acid in an amount of about 10% by weight has been used as a cleaning fluid for effectively removing Mn3O4-based filter cakes. However, when reacted with Mn3O4, citric acid has been known to dissociate insoluble manganese citrate causing formation damage in the wellbore, and therefore is not a suitable composition to effectively dissolve or remove the Mn3O4-based filter cake from the wellbore while preventing formation damage.
Therefore, what is needed is a filter cake removal composition which dissolves, and more preferably removes, a filter cake generated by a manganese-tetraoxide-based drilling fluid without causing formation damage in the wellbore.